Lightweight support structures have, in the past, been used to provide a frame for "sling"-type chairs, i.e., chairs in which the seating surface consists of a piece of flexible fabric supported either at its four corners or along two nonadjacent sides. The fabric is usually sized such that, when attached to the frame, it is not taut, but drapes somewhat and thus provides both posterior and back support.
Often the support structure has been made up of a number of support members which are pivotably attached to one another, such that the chair may be collapsed for transportation, etc. Fenby, U.S. Pat. No. 244,216 and Morgan, U.S. Pat. No. 2,689,602 disclose such support structures.
More recently, support structures constructed solely of pure tension members and pure compression members have been devised. The pure compression members are commonly struts (e.g., poles), the ends of which are interconnected by the pure tension members, usually cables or ropes. Support structures of this type, examples of which are to be found in Miller, U.S. Pat. No. 4,148,520 and Wiesner, U.S. Pat. No. 3,901,551, have been termed "tensegrity" (or "tensional-integrity") types of structures.
The term "tensegrity" was apparently coined by Buckminster Fuller, to describe structures which, as described in Fuller, R. B., Synergetics, Collier MacMillian (1975), have the ability "to yield increasingly without ultimately breaking or coming asunder". Such structures inherently lack rigidity. A more comprehensive treatment of tensegrity is to be found in the above referenced work.
Rocking chairs have been provided by support structures having two rigid (i.e., compression) members that each have upper end portions that are spaced from each other and lower end portions that are spaced from each other. The rigid members are oppositely inclined with respect to the horizontal, intersecting each other in side view, and one of the rigid members is positioned intermediate the other. The rigid members are connected to each other near their bottoms by one pair of flexible tension members and above where they intersect by another pair of flexible tension members, and the rigid members can pivot about their points of contact with the ground providing the rocking movement. Examples of such support structures are disclosed in Meeker, U.S. Pat. No. 1,969,313; Robeson, U.S. Pat. No. 4,118,064; and Gilbert, U.S. Pat. No. 4,251,106. Meeker and Robeson teach that the structures can be modified to prevent rocking by adding pin connections between the rigid members where they intersect, and Gilbert discloses preventing backward pivoting beyond a certain point by interference of the rigid members and preventing forward pivoting beyond a certain point by a pair of cords between the rigid members.